A. Field of the Invention
The present invention relates to apparatus and methods for light pollution (e.g., glare, spill, and sky glow) control for high intensity discharge lighting fixtures and in particular, for wide area lighting, such as sports lighting; and achieving full or near full cut-off at or near normal aiming angles for such lighting fixtures.
B. Problems in the Art
What is sometimes called light pollution (e.g., glare, spill light, and sky glow or uplight) is of significant concern for wide area lighting. Adjacent home and business owners many times complain about light pollution from wide area lighting systems. These types of light pollution are well-known in the art and discussed in such publications as the Illumination Engineering Society of North America (IESNA), Sports and Recreational Area Lighting, publication RP-6-01; Bullough, J. D. (2002), “Interpreting Outdoor Luminaire Cutoff Classification” Lighting Design+Application 32(7):44-46; Commission Internationale de l'Eclairage (CIE), “Guide on the limitation of the effects of obtrusive light from outdoor lighting installations”, Report TC5.12, Vienna; Commission Internationale de l'Eclairage (CIE) (1997) “Guidelines for Minimizing Sky Glow” Vienna; Illuminating Engineering Society of North America (IESNA), 2000. American National Standard Practice for Roadway Lighting, ANSI/IESNA RP-8-00, New York; Illuminating Engineering Society of North America, Illuminating Engineering Society of North America (IESNA), 1999, Recommended Practice for Outdoor and Environmental Lighting, IESNA RP-33-99, New York; Illuminating Engineering Society of North America; Rea, M. S., ed. 2000, IESNA Lighting Handbook: Reference and Application, 9th edition, New York: Illuminating Engineering Society of North America; which all are incorporated by reference herein.
The owner of the present application has patented a variety of ways to address these types of problems. Examples are: U.S. Pat. Nos. 4,947,303; 5,161,883; 5,211,473; 5,816,691; 5,856,721; and 6,203,176, all of which are incorporated by reference herein.
Most times there is a delicate balance between light pollution control methods and avoiding significant reduction in the amount of useable light output from such fixtures. Of course, complete light pollution control can be achieved by essentially blocking most light from a lighting fixture. This is impractical, however, as it effectively wastes the energy used to produce light from that fixture, and requires many such fixtures to provide adequate light to most targets. Another method is aiming fixtures at steep angles down from horizontal, however this greatly limits the fixture's use because many applications, including sports lighting, require projecting light from the fixtures at angles to cover parts of the target area (e.g., sports field) that are substantial distances away from the fixtures and, as such, must be aimed at shallower angles.
The above-mentioned patents present several ways in which this balance is approached. Many of the patents reduce light pollution without substantial decrease (and sometimes increase) of usable light to the target area. The laws of physics, however, make it difficult to achieve what is known as “full cut-off”, or even near-full cut-off, while maintaining reasonable efficiency from the fixture.
There are certain cases, though, where drastic light pollution control is needed. With certain fixtures that are aimed in sensitive directions, the present state of the art for light pollution control uses fixtures and techniques that tend to materially diminish light intensity usable to the target.
There is, and continues to be, a need in the art for light pollution control solutions, including those that require what might be called drastic light pollution control; perhaps for a few fixtures with special light pollution control needs.
For example, there are times when full cut-off is needed, (e.g., to meet full cut-off technical specifications, such as for example, the IESNA definition of what is considered full light cut-off (see IESNA Publication RP-33-99, entitled Recommended Practice for Outdoor and Environmental Lighting (copyright 1999), p. 17, incorporated by reference herein)). As can be seen in the definition, “full light cut-off” is defined as a fixture that produces zero candela intensity above a certain plane (i.e., 90° above nadir) and no more than 100 candela (cd) per 1000 lamp lumens at a vertical angle of 80° above nadir (see FIG. 12 herein). For a typical sports lighting aiming axis, the plane is normally considered horizontal. The definition in the published “IESNA Lighting Handbook 9th edition” from IESNA, incorporated by reference herein, states no intensity can extend above, in that case, a horizontal plane at or near the fixture. Therefore, a fixture that meets this definition must prevent light from the source that otherwise would tend to travel above the plane from traveling above that plane.
As mentioned, the long-time problem with full cut-off fixtures is they tend to severely block or absorb light from the light source of the fixture to meet the full cut-off definition, or they must be aimed steeply downward; the appeal is that it is much easier to achieve full cut-off if little light comes out of the fixture and/or it is aimed at steep angles down to the ground. The fixture in the diagram of FIG. 12 herein is essentially pointed straight down (to nadir or 90° down from horizontal) and has an enclosure around the light source except for a bottom opening. As can be appreciated, the enclosure prevents direct light from traveling above the horizontal plane through the fixture. Even light reflecting from an interior surface of the fixture, a lens over the opening, or other parts of the enclosure would have a hard time traveling above that plane. However, as mentioned previously, it is not very often that such fixtures are practical for large area lighting, such as sports lighting; fixtures which need to throw light over a greater distance (see FIGS. 6A-C) to project light to different areas of a field. Typical aiming angles for such lighting fixtures are 45° to 60° above nadir (or 30° to 45° down from horizontal) and sometimes 60° to 75° above nadir (15° to 45° down from horizontal). As can be appreciated, this tilts the fixture more in a direction parallel to the horizontal plane through the fixture, thus making it much more difficult to achieve the full cut-off definition, or even near-full cut-off. Both direct light and reflected light from the fixture are problems in this regard.
As also mentioned, the technique of blocking a substantial amount of light from the fixture to try to achieve some level of cut-off is very inefficient. For the amount of electricity used, a low ratio of useable light to the target is normally produced. This inefficiency tends to increase as the fixture is modified more towards full cut-off.
Therefore, there continues to be a need in the art for solutions to a variety of lighting problems, specifically those that need a substantial amount of full or near-full light cut-off. There are also times when near-full cut-off is needed at normal sports lighting type aiming angles.